U.S. Republican presidential hopefuls said Saturday at a debate in the southeastern state of South Carolina that President Barack Obama should not nominate a replacement for late Supreme Court Justice Antonin Scalia, and instead leave the matter for his successor.

Businessman Donald Trump, who leads in national polls, called Scalia's death hours before the debate a blow to conservatism in the United States and said it is up to Senate Majority Leader Mitch McConnell to delay the nominating process so that a justice cannot be confirmed before Obama leaves office next January.

The candidates are trying to convince voters in South Carolina before the state's primary election on February 20, as they try to amass the support necessary to become the Republican Party's nominee for president.

National security

The debate became testy on the issue of national security, with Trump attacking Bush based on the record of his brother, George W. Bush, who served as president before Obama.

Trump said the war in Iraq "was a big fat mistake." When Bush and Rubio asserted that George W. Bush's actions made America safer, Trump repeatedly mentioned the destruction of the World Trade Center during the September 11, 2001 terror attacks in New York.

Bush also criticized Trump's stated support for Russian President Vladimir Putin, saying it is "ludicrous" to suggest Russia can be a positive partner in the conflict in Syria.

Immigration plans

Immigration brought more exchanges, particularly between Rubio and Cruz. Rubio advocated a focus on first addressing illegal immigration, saying no other programs will be effective unless the government proves that methods to secure the borders are working.

On illegal immigrants already in the country, Rubio said he thinks the American people will be "reasonable but responsible" about someone who has been in the U.S. for a long time.

Cruz asserted his plans are different, saying he does not support any path to citizenship for illegal immigrants already in the U.S.

Ohio Governor John Kasich, who finished second in the New Hampshire primary, said he favors a path to legalization but not citizenship, as well as sealing the border and a guest worker program..

He also spoke out against the attacks engaged in by the rest of the field, saying that tenor is going to lose them the election in November. He advocated stopping attack ad and simply saying what they stand for.